The overall goal of this study is to examine predictors of weight gain (low total energy expenditure [EE] adjusted for body composition, low resting EE, low habitual EE from physical activity, and low rates of fat oxidation) in prepubertal nonobese females. This study will provide valuable information for understanding which factors that predispose certain individuals to obesity. This information is crucial to the development of strategies for the prevention of obesity starting in childhood. We will test the following hypothesis: Low total energy expenditure (TEE), adjusted for body composition, will predict relatively rapid weight gain in pre-obese children; Low resting EE and low habitual EE from physical activity will predict more rapid weight gain in pre-obese children; Low rates of fat oxidation will predict relatively rapid weight gain in pre-obese children. The specific aims to test this hypothesis are: To examine the total EE (adjusted for body composition) and the rate of fat oxidation in childlren of obese and nonobese parents; To examine the components of EE in children of obese and nonobese parents; To examine the within-child variability in EE determinations by two different methods when duplicate measurements by each method are obtained; To determine the changes in body composition and fat patterns; To determine the effect of changes in body composition and fat patterns on blood pressure and glucose tolerance.